University of California Water Resources Center

A study of the effects of streamflow regulation on riparian vegetation focused on seedling establishment along 30 low-gradient, alluvial streams throughout central California. Initial establishment densities were generally lower on regulated streams than along non-regulated ones. However, prolific establishment occurred on the recently regulated streams as the vegetation adjusts to new stream conditions. Seedling survival was slightly greater on regulated streams than non-regulated ones following the 1985-1986 flooding. Survival was much higher on both regulated and non-regulated streams during the year of low discharges (1986-1987).

Seedling survival and growth were monitored in a controlled experiment simulating regulated and non-regulated conditions. Survival did not vary considerably among species. Growth was less in the fluctuating water level treatment than under simulated non-regulated conditions. Growth was higher for all four common species under the fluctuating treatment in a gravelly substrate but lower for cottonwood and sandbar willow in a sandy substrate.